Patients with cystic fibrosis who used the ThAIRapy vest for their pulmonary care were enrolled. Serum prolactin levels were measured at 0,15 and 30 minutes during a vest treatment. This was done to determine whether baseline prolactin levels were normal and whether there was an acute rise in serum prolactin associated with the vest treatment. Patients were also asked to fill out a questionnaire designed to elicit symptoms of hyperprolactinemia.